Electrically adjustable pieces of furniture are being offered more and more. For example, in the case of many desks, especially in the case of writing desks, the height of the desk surface is electrically adjustable by means of a special drive. Also beds, for example, adjustable beds or hospital beds, could be set by means of electrical drives, for example, in height or inclination angle of the bed.
Here, for the driving of the electrical adjustment device, it is possible to use direct-current motors that are operated with a low voltage. For this purpose, the mains voltage is stepped down, for example, by a transformer into the lower voltage range of the direct-current motors and converted into a direct-current voltage by means of a rectifier circuit. The control of the direct-current motors is performed in an associated control through a controlled connection of the motors to the direct-current voltage. As an alternative to the transformer, such a control could also be supplied with the required direct-current voltage by a switch-mode power supply.
Another possibility for driving of an electrically adjustable piece of furniture lies in the use of one or more alternating-current motors for which a control is likewise provided. In this case, for the control, the mains alternating-current voltage is transformed down into a lower alternating-current voltage range, in order to connect the alternating-current motors to the down-transformed alternating-current voltage in a controlled way. Alternately, for controlling the alternating-current motors, an alternating-current voltage could be derived from a direct-current voltage that is provided by means of an external switch-mode power supply.
For the use of an external switch-mode power supply, it is necessary to attach the control and switch-mode power supply separately or each individually, that is, with a higher production expense, to the adjustable piece of furniture.
The production expense and the operating costs of a control are also influenced by the power requirements of the control.
Transformers for stepping-down the mains alternating-current voltage typically have, due to the required power, such spatial requirements that an integration of the transformers in a housing together with a control causes large housing sizes. Such structural sizes, however, could make the arrangement or fastening of a control on a piece of furniture to be adjusted more difficult and cause high costs.